The present invention relates to a device for detecting the mechanical state of a machine element that can rotate about an axis.
Agricultural working machines, such as tractors, harvesting machines, attachments and the like, utilize rotatable machine elements, in particular, (drive) shafts in highly diverse application forms in order to drive highly diverse assemblies and, very generally, in order to transfer mechanical drive power between these assemblies. In this connection there is often a need, depending on the particular application, to detect the torque transferred by the machine element (a shaft, in particular), as is the case in other fields of mechanical engineering.
As known, this can take place by detecting the torsion of the machine element itself. Torsion, which is the elastic twisting of the machine element, can be used to calculate a torsional moment that is acting on the machine element, provided the material properties and geometry of the machine-element are known. In the case of a shaft, for example, this approach can be used to determine the torque that is transmitted by the shaft, the magnitude of which corresponds to the torsional moment acting on the machine element.
The torsion of a rotating machine element can be detected, in principle, by a stationary sensor arrangement that very exactly determines the respective angle of rotation of the machine element at two regions of the machine element that are spaced axially apart from one another. The torsion of the machine element is determined by simultaneously comparing the angles of rotation in the spaced-apart regions. The disadvantage of this method is the amount of outlay that is required, in terms of installation space and costs, to detect the angle of rotation at two points that are spaced apart from one another. In addition, performing an exact measurement at relatively high rotational speeds is either not possible or requires considerably complex measurement technology.
It also is possible to detect the torque transferred by the machine element by measuring torsion at the rotating machine element, for example, using strain gauges that are suitably disposed for this purpose. A disadvantage of this type of detection, however, is the difficulty of transmitting the measurement signal from the rotating measurement point correctly and without interference.
Moreover, reference is made to DE 37 08 103 A1 with regard to another type of torque determination. FIG. 7 therein shows, for example, a device for detecting the torsion of a shaft. To this end, an annular actuator is disposed on the shaft so as to be axially displaceable and is connected at both ends by an elastic helical structure at each end (said helical structures turning in opposing directions), to regions of the shaft that are spaced axially apart from one another.
A torsion of the shaft caused by a torque transferred by the shaft results in a displacement of the centrally disposed actuator in the axial direction. The displacement increases as the torsion increases and decreases as the torsion decreases, and therefore, the extent of the displacement of the actuator can be considered to be a measure of the torsion. Using a sensor, e.g., inductive detection of the displacement of the actuator, it is possible to determine the torsion of the shaft and a torque that is transferred by the shaft in this manner.
For numerous control/regulating processes on agricultural machines, it is often desirable in practical applications to know not only the torque that is transferred by a machine element, but also the speed thereof. Speed is typically determined using a separate sensor system (speed sensor). This requires installation space and, due to the measurement technology that is required, generates costs that are not inconsequential.